Outbox vs CDC: A Decision Matrix for Event‑Driven Microservices

Deep Dive: Stage 1 — The Three Strategies

Observable outcome: You can explain how “The Three Strategies” changes the architecture or implementation path.

Deep Dive: Stage 2 — Decision Matrix: When to Pick Each

Observable outcome: You can explain how “Decision Matrix: When to Pick Each” changes the architecture or implementation path.

Deep Dive: Stage 3 — Quick Implementation Sketch (Transactional Outbox with Spring Data JPA)

@Entity
@Table(name = "orders")
class Order {
  @Id @GeneratedValue Long id;
  String status;
  // …
}

@Entity
@Table(name = "outbox_events")
class OutboxEvent {
  @Id @GeneratedValue Long id;
  String aggregateType;
  Long aggregateId;
  String payload; // JSON
  Instant createdAt;
}

@Service
class OrderService {
  @Transactional
  void placeOrder(Order order) {
    orderRepository.save(order); // domain write

    // outbox write in same tx
    OutboxEvent e = new OutboxEvent();
    e.setAggregateType("Order");
    e.setAggregateId(order.getId());
    e.setPayload("{\"orderId\":" + order.getId() + "}");
    e.setCreatedAt(Instant.now());
    outboxRepository.save(e);
  }
}

A lightweight worker polls outbox_events and publishes to Kafka, then marks the row as sent or deletes it. The key is that the DB transaction guarantees the order write and the outbox row are committed together.

Observable outcome: The key is that the DB transaction guarantees the order write and the outbox row are committed together.

Deep Dive: Stage 4 — Architecture Kit Diagram

Observable outcome: You can explain how “Architecture Kit Diagram” changes the architecture or implementation path.

• Transactional Outbox is the gold‑standard for strong consistency.
• Outbox is great for simpler, low‑latency needs.
• Apply transaction-isolation-distributed-acid to The Three Strategies.
• Apply transactional-outbox-pattern to Decision Matrix: When to Pick Each.
• A lightweight worker polls outbox events and publishes to Kafka, then marks the row as sent or deletes it.